Patent Document 1 discloses a device that collects an ambient sound outside a car with a sound collector and presents the collected sound. The device can present a sound obtained by suppressing an ambient sound in a moving direction of a vehicle, present a sound obtained by suppressing an ambient sound in a direction of a sight line of a driver, present a sound obtained by suppressing a frequency band of running noise in the car, adjust a sound pressure level in accordance with vehicle speed information, or start presenting a sound in response to detection of a mobile sound source.
Patent Document 2 discloses a system in which a sound generation device provided for an ambulance, a fire engine, a railroad cross, and the like and an in-vehicle audio notification device that notifies the inside of the car of a sound generated outside the car are provided. The sound generation device outputs a predetermined sound on the basis of a signal obtained by superimposing identification information indicating the type of an audio signal on the audio signal. The in-vehicle audio notification device extracts the identification information from the collected audio signal. The in-vehicle audio notification device determines whether a notification for the inside of the car is performed, on the basis of the extracted identification information.
Patent Document 3 discloses a device that collects an ambient sound outside a vehicle with a sound collector and presents the collected sound. The device detects an object around the own vehicle. In a case where the object is detected, the device presents a predetermined sound. In a case where the object is not detected, the device does not present the predetermined sound. The predetermined sound is obtained by synthesizing a sound collected by a microphone and a virtual sound generated by the device. In a case where the detected object is an object that makes a sound, the detection of the object is notified by the sound collected by the microphone. In a case where the detected object is an object that does not make a sound, the detection of the object is notified performed by the virtual sound.
Patent Document 4 discloses a device that detects an approaching vehicle approaching the own vehicle, on the basis of the collected sound outside the vehicle. The device detects the shape of a traveling road on which the own vehicle travels, the type of a road surface of the traveling road on which the approaching vehicle travels and adjusts sound collection characteristics on the basis of the detection result.